1. Field of the Invention
The present invention relates to an optical tomographic apparatus and a control method thereof. For example, the present invention relates to an optical tomographic apparatus used for ophthalmic care, and a control method thereof.
2. Description of the Related Art
In recent years, an optical image measurement technology for forming images of a surface and an inside of an object to be measured through use of light has been drawing attention. The optical image measurement technology has no invasiveness to a human body unlike a conventional X-ray CT, and hence, its application to a medical field, in particular, is being expected. Above all, its application to an ophthalmic field is advancing remarkably.
As a typical procedure of the optical image measurement technology, there is a procedure called Optical Coherence Tomography (OCT). According to this procedure, owing to the use of an interferometer, measurement with high resolution and high sensitivity can be performed. There is also an advantage in that safety to a subject is high owing to the use of extremely weak light in a wide band as illumination light.
An optical tomographic apparatus using the Optical Coherence Tomography (OCT) utilizing optical interference (hereinafter referred to as “OCT apparatus”) is an apparatus capable of acquiring a tomographic image of a sample with high resolution, and particularly, relates to an anterior ocular segment optical tomographic apparatus for forming an image of an anterior ocular segment of, an eye to be inspected.
The OCT apparatus is capable of irradiating a sample with measuring light that is low coherent light and measuring backscattered light from the sample with high sensitivity through use of an interference system or an interference optical system. Further, the OCT apparatus can acquire a tomographic image with high resolution by scanning the sample with the measuring light. Thus, a tomographic image of a cornea site in an anterior ocular segment of an eye to be inspected is acquired and utilized in ophthalmic diagnosis and the like.
In such an ophthalmic apparatus, in order to take an image, an inspection portion (mainly, a measurement optical system) of the apparatus is matched with an anterior ocular segment cornea site of an eye to be inspected and an imaging position of an interference optical system, and the eye to be inspected and the apparatus are aligned at a predetermined length.
Japanese Patent Application Laid-Open No. 2009-22502 describes a cornea observing apparatus capable of grasping a depth position of an image in a cornea and determining an abnormal state of a cell of the cornea. In the cornea observing apparatus, in order to take an image of each site of a cornea epithelium, a Bowman's layer, a corneal stromal layer, a Descemet's layer, or a cornea epidermis of an anterior ocular segment, a reference mirror is moved. Further, a distance between an eye to be inspected and a cornea observing apparatus is set to a predetermined length regarding each photographing site, and the reference mirror is moved to perform actual photographing.
Further, Japanese Patent Application Laid-Open No. 2011-147612 describes an optical tomographic apparatus capable of taking both an anterior ocular segment tomographic image and an eyeground tomographic image. This apparatus is an ophthalmic photographing apparatus that involves moving a reference mirror in an interference optical system to move a photographing position of the interference optical system to a predetermined position in accordance with an anterior ocular segment photographing mode and an eyeground photographing mode. The ophthalmic photographing apparatus has a configuration in which the reference mirror is moved to a predetermined position in an anterior ocular segment photographing mode, and at that time, a distance between an eye to be inspected and the ophthalmic photographing apparatus is set to a predetermined length.
In this case, when an attempt is made so as to acquire a tomographic image of a desired site in an anterior ocular segment, it is generally necessary to obtain a state in which the desired site is present in a portion corresponding to an imaging position by moving a fixation lamp and further to obtain an appropriate focus state. In this case, a burden on a subject or difficulty in operation for obtaining the expected state cannot be avoided. Further, as another aspect, it is also conceivable to cleave a desired site from a taken tomographic image and electronically sharpening the site. However, a decrease in resolution involved in enlargement, an increase in time required for sharpening, and the like cannot be avoided.